Potentiometer-rheostat



Aug. 23, 1960 F. M. BROWN 2,950,455

POTENTIOMETER-RHEOSTAT Filed Nov. 24, 1958 A 90 N4 //6 //2 H64 7 Franklin M Brown IN V EN TOR.

L Fig: 4.

United States Patent 2,950,455 POTENTIOMETER-RHEOSTAT Filed Nov. 24, 1958, Ser. No. 776,010

15 Claims. (Cl..338134) This invention pertains to voltage dividers, and relates particularly to the novel and simplified construction of a voltage divider which affords increased convenience of operation and accuracy of performance both as a po-' tentiometer and as a rheostat.

It is a principal object of the present invention to provide a precision voltage divider, usable as a potentiometer or as a rheostat, and in which the values of voltage may be read directly upon concentric operating dials.

Another important object of this invention is to provide a potentiometer-rheostat which is of minimum size for maximum facility of integration with other instrument components, and yet affords maximum 'heat dissipation and therefore maximum wattage uitlization.

Still "another important object of the present invention is the provision of a potentiometer-rheostat which accommodates use of fixed resistances, thereby affording maximum frequency response and linearity and permit-- ting pre-stabilization of the resistances to insure maximum accuracy over a long operating period.

A further important object of this invention is the provision of a potentiometer-rheostat which is of simplified construction for economical manufacture, which requires but a single hole for mounting on a panel, and which is operated with maximum facility and precision.

The foregoing and other objects and advantages of this invention will appear from the following detailed description, taken in connection with the accompanying drawing in which like parts are identified by like reference numerals, and in which:

Fig. 1 is a plan view of a potentiometer-reostat construction embodying the features of the present invention, portions thereof being broken away to disclose details of construction;

Fig. 2 is a front plan view of the concentric operating dials as viewed from the top in Fig. 1;

Fig. 3 is a fragmentary sectional view taken along the line 33 in Fig. 1; and

Fig. 4 is a mechanical-schematic diagram of the elec trical circuit employed in the assembly illustrated in Fig. 1.

Referring particularly to Fig. 1 of the drawing, the assembly includes a frame comprising a pair of parallel rods maintained in laterally spaced relation by the transverse rear end plate 12, the detent plates 14 and 16, and the cap 18. Supported on the rods 10 are the switch assemblies 20 and 22, disposed between the detent plates 14 and 16, and the switch assemblies 24 and 26 disposed between the detent plate 14 and the rear end plate 12. These plates and switch assemblies are maintained in longitudinally spaced relation by means of interposed lengths of spacer sleeves 28 carried by the rods. The sleeves preferably are of electrically non-conductive material- The assembly of these components, together with the cap 18, is drawn into firm engagement by tightening the nuts 30 upon the threaded ends of the rods.

ice

A hollow externally threaded bushing 32 extends through the axial center of the forward detent plate 16 and cap 18 and is secured firmly to the plate. Extending axially through this bushing is a hollow shaft 34 which supports at its forward end the outer operating dial 36. The rear end of the shaft extends through central openings 34 in the central rotary sections and 22' of the switch assemblies 20 and 22, respectively. The outer periphery of this end of the shaft is noncircular in cross section to match the non-circular openings in the rotary sections, whereby to secure them together for simultaneous rotation.

A second hollow shaft 40 extends through the hollow outer shaft 34 and supports at its forward end the intermediate operating dial 42 which nests freely within a central depression formed in the outer dial. The projection 44 extending from the intermediate dial functions as a handle by which to manipulate it. The rear end of the shaft 40 is made non-circular in outer cross section and extends through the non-circular openings 40 in the central rotary sections 24 and 26 of the switch as semblies 24 and 26, respectively, for simultaneous rotation.

A third shaft 46 extends through the hollow second shaft 40 and supports at its forward end the operating knob 48, secured thereto as by means of the Allen screw illustrated. The knob is secured firmly to the inner dial 50 which nests freely Within a central depression formed in the intermediate dial. The rear end of the shaft 46 extends through the rear plate 12, and supports the electrical contact arm 52 of potentiometer 54.

The potentiometer comprises a resistance wire 56 wound helically about an annular ring of electrically non-conductive material, and contained within an electrically non-conductive casing 58 supported upon the rear end plate 12. The contact arm 52 is arranged for slid ing contact with the circular band of resistance wire as the inner shaft 46 is rotated by the control knob.

Referring now particularly to Fig. 3 of the drawing, each of the central rotary sections 20, 22, 24' and 26' is associated with a fixed section 20", 22", 24" and 26" respectively, and each is mounted for rotation within a central opening in the fixedsection. Both the rotary sections and fixed sections of each switch assembly are made of electrically non-conductive material. Electrica-lly conductive collector rings 60 and 62 are mounted on opposite sides of each rotary section of each switch assembly, the rings preferably projecting radially outward from the rotary section a distance sufficient to overlap the associated fixed section and thus confine the rotary section therein. The rings 60 and 62 on each rotary section are connected together electrically as by the rivet 64 extending through openings in the rotary section. This connection is indicated in Fig. 4 by conductor 64.

Projecting radially from the collector ring 60 of each rotary section is a brush 60' which is disposed for sliding engagement selectively with a plurality of contact elements 66 mounted upon the fixed section of the switch. The contact ends of these elements are disposed at spaced circumferential intervals about the rotary section. An additional contact element 68, hereinafter referred to as the feed contact, is mounted on the fixed section of the switch and is provided with a contact end which is in permanent sliding engagement with the collector ring 60.

Projecting radially from the periphery of the collector ring 62 of each rotary section are a plurality of electrically conductive brushes 62, arranged at uniformly spaced intervals about the circumference of the ring. These brushes are disposed for sliding engagement with a single contact element 70 mounted upon the fixed sectionof the switch.

In accordance with the present invention, the arrangement of brushes and contacts associated with each switch assembly is such that, during rotation of the rotary section, the brush '60 on collector ring 60 maintains electrical engagement with a given-contact 66 during such movement of the other collector ring 62 as will move its spaced brushes 62' between one position in which a brush is in electrical contact with the contact 70 and a second position in which said contact '70 is disposed between the brush 62 it just left and the next adjacent brush.

Means is provided to insure that the rotary sections of eachswitch assembly are rotated in precise increments so that the contact 70 isplaced alternately in electrical engagement with a brush 62 and centrally between and out of engagement with adjacent brushes, while simultaneously maintaining the brush 60' of that same switch assembly in electrical engagement with a given contact 66. The means illustrated in the drawing and the best shown in Fig. 1 includes the detent plates 14 and 16 referred to hereinbefore. Associated with each of these plates is a ring-shaped leaf spring 72 which carried one or more detent balls 74 and which functions to urge the ball toward the circumferentially spaced pockets 76 formed in the detent plate. to and rotates with shaft 34, and the other leaf spring is secured to and rotates with shaft 40. The pockets in each detent plate are arranged in such manner that when the ball is seated in successive pockets the contact 70 is posi-.

tioned successively in electrical engagement with a brush 62' and centrally between and out of electrical engagement with adjacent brushes, and brush 60' maintains engagement with a given contact 66 during said single stepmovement of the rotary sections.

Referring now to Fig. 4 of the drawing, the contact elements 66 mounted on one side of the fixed section 20" of switch assembly 20 serves to support and interconnect the four fixed resistances 80 in a series arrangement. Similarly, the contact elements 66 on one side of the fixed sections of switch assemblies 22, 24 and 26 support and serially interconnect the fixed resistances 82, 84 and 86, respectively. As will be discussed more fully hereinafter, the resistances 80 and 82 are equal in value and number, thereby forming a matching pair of series connected chains. Similarly, the resistances S4 and 86 are equal in value and number and form a second matching pair of series chains. The value of each resistance 84, 86 is onetenth the value of each resistance 80, 82.

The feed contact 68 permanently engaging the collector ring 60 of switch assembly 20, is connected through the fixed interpolating resistance 90 to the single contact 70 associated with the collector ring 62 of the same switch assembly 20. In similar manner, the feed contacts '68 and single contacts 70 associated with switch assemblies 22, 24 and 26, are interconnected through fixed interpolating resistances 92, 94 and 96, respectively.

The potentiometer resistance 56 is chosen to be the same value as the fixed interpolating resistances 94, 96 associated with the last succeeding matching pair of series chains 84, 86. One end of the potentiometer resistance 56 is connected through wire 100 to the single contact element 70 associated with switch assembly 26. The opposite end of the potentiometer resistance is connected through wire 102 to the single contact element 70 associated with switch assembly 24. One end of the series connected resistances 86 associated with switch 26 is connected through wire 104 to one end of the series connected resistances 82 associated with switch assembly 22. Similarly, one end of the series connected resistances 84 of switch assembly 24 is connected through wire 106 to one end of the series connected resistances 80 of switch assembly 20. Wires 108 and 110 connect the single contact elements 70 associated with switch assemblies 21) One leaf spring is secured.

and 22, respectively, to terminal posts 112 and 114 respectively. The potentiometer contact arm 52 is connected to the terminal post 116 through wire 118. The terminal posts are supported conveniently upon the cap 18.

It is to be noted that the arrangement of the resistance chains, interpolating resistances, potentiometer and switch contacts provides a series circuit. It is to be noted further that by this arrangement each matching pair of series shorted out of series connected arrangement with one or more of the associated series connected resistances, selectively as the associated control shaft is manipulated. The

resistance value of the fixed interpolating resistance is chosen to be one-half the resistance of each of the series connected resistances associated therewith. In this man? ner the five fixed resistance elements associated with each switch assembly serves the same function as ten seriallyconnected resistances.-

It is to be noted that the fixed resistances are mounted upon the contact elements carried by the fixed sections of the switch assemblies, in longitudinally spaced relation and in a radial pattern about the coaxial shafts. This arrangement is chosen for illustration, in order best to expose all of the parts of the assembly to view. In actual practice, however, it is preferred that the resistance elements on adjacent switch assemblies overlap, in order to reduce the length of the assembly to a minimum. Either arrangement has the advantage of reducing the periph eral dimension of the assembly to a minimum while ofiering maximum efiiciency in heat dissipation.

It will be observed that the voltage divider construction described hereinbefore affords maximum facility in mounting on an instrument panel 120. The only requirement is a single hole in the panel to receive the bushing 32. A pair of lock nuts 122, located on opposite Sides of the panel, then are tightened upon the threads of the bushing, whereupon the instrument is secured firmly to the panel. tion of the device, is of particular advantage when the device is to be integrated with other components in a common housing, such as in the assembly of a computing machine or other electrical measuring instrument.

A typical construction of the potentiometer-rheostat de scribed and illustrated hereinis as follows: The interpolating potentiometer resistance 56 is 100 ohms; each of the series connected resistances 84 and 86 is 200 ohms and each of the fixed interpolating resistances 94 and 96 associated therewith, is 100 ohms; each of the series connected resistances and 82 is 2000 ohms and each of the fixed interpolating resistances and 92 associated therewith, is 1000 ohms.

By the foregoing arrangement it is possible to calibrate the operating dials 36, 42 and 50 to provide a direct indication of the decimal fraction of voltage output. calibrations illustrated afford precise readings to four decimals, and the fifth place may be estimated with a high degree of accuracy. Each of the operating dials is keyed to its supporting shaft in such manner that the dial calibrations are properly oriented with respect to the brush and contact positions on the associated switch assembly. This greatly facilitates installation of the dials on the shafts. v

To facilitate reading of the dials, it is preferred that an index marker or line be associated therewith. In the embodiment illustrated the index comprises a base mem- This feature together with the compact construc Thev her having an inner section 124 provided at its inner end with a perforation by which it may be mounted upon the bushing 32 and secured thereto in the desired position of circumferential adjustment by means of the lock nut 122. The outer end 126 of the base member is offset outwardly, substantially normal to the inner section, and lies adjacent the outer periphery of the outer operating dial 36.

The inner section 126 of an angularly bent transparent index plate closely overlies the operating dials and, if desired, carries a hair line 130 which extends in the radial direction of the operating dials. 132 of the index plate overlies the outer bent section 126 of the base member, and is provided with a longitudinal slot 134 for receiving the set screw 136 mounted in a tapped opening in the outer bent section of the base member. The longitudinal slot permits adjustment of the index plate to accommodate variations in distance between the outer surface of the operating dials and the inner section of the base member.

A cylindrical can 140 encloses the major portion of the apparatus and functions by connection with the cap, such as by the screws illustrated, to seal and electrically shield the apparatus therein.

In using the device as a potentiometer, terminals 112 and 114 provide a fixed input and terminals 114 and 116 provide a variable output. Terminals 1'12 and 116 also may be used for output, in which case the numerical dial markings illustrated are read inversely. In using the device as a rheostat, connections are made to terminals 114 and 116. If terminals 112 and 116 are used, the dial markings are read inversely.

There are many inherent advantages in the voltage divider construction described hereinbefore: The novel mechanical arrangement utilizes a minimum number of resistance elements, and yet affords full range operation either as a potentiometer or as a rheostat. The use of fixed resistances and the provision of the switch positioning detent assemblies, assures a very high degree of accuracy in reproducing any desired voltage reading.

The compact arrangement of concentric calibrated dials afiords rapid adjustment to any position. The combination of dials provides an exceptionally long calibrated scale by which to obtain maximum accuracy of reading. The scale readings are made in the same manner as the digits would be written, thereby eliminating possible confusion and error.

The mechanical arrangement of fixed resistances operated by coaxial shafts from concentric dials provides a construction which is very compact but yet highly efiicient in the dissipation of heat. The mechanical arrangement affords rapid and accurate assembly, thereby minimizing the cost of manufacture.

It will be apparent to those skilled in the art that various changes may be made in the structural details described hereinbefore. For example, the number and magnitude of units of fixed resistances and the corresponding number of concentric dials, may be varied as desired. Additionally, the number of resistances in each series chain and the number of associated brushes, also may be varied. Although the interpolating potentiometer resistance is illustrated herein as being a continuous wire, it will be apparent that a conventional carbon type resistance may be employed, or that the potentiometer may comprise a series of fixed resistances.

The foregoing and other changes may be made as desired, without departing from the spirit of this invention and the scope of the appended claims.

Having now described my invention and the manner in which the same may be used, what I claim as new and desire to secure by Letters Patent is:

l. A potentiometer-rheostat comprising a first series chain of resistances of equal value, .a second series chain of resistances of equal value and matching the first series chain, first rotary switch means associated with the first The outer bent section series chain, second rotary switch means associated with the second series chain and arranged coaxial with the first rotary switch means, and a rotary operating shaft interconnecting the first and second rotary switch means for simultaneous rotation thereof with the rotary operating shaft, the matching pair of first and second series chains and associated rotary switch means being included in series in an electric circuit in such manner that as the switch means of one series chain of the pair is operated to increase the resistance in the electric circuit the rotary switch means of the other series chain of the pair is operated simultaneously to decrease the resistance in the electric circuit by an equal amount.

2. The potentiometer-rheostat of claim 1 including an interpolating potentiometer connected at its opposite ends to the rotary switch means associated with the first and second series chains, respectively, and including a rotary section arranged coaxial with the rotary switch means, and a rotary operating shaft connected to the rotary section of the potentiometer and arranged concentric with the operating shaft for the rotary switch means.

3. A potentiometer-rheostat comprising a plurality of first series chains of resistances, the resistances in each chain being of equal value and the resistances in succeeding chains being a fractional value of the resistances in the neat preceding chain, a plurality of second series chains of resistances each matching a corresponding one of the plurality of first series chains, first rotary switch means associated with each first series chain, second rotary switch means associated with each second series chain and arranged coaxial with the first rotary switch means, the matching pairs of first and second series chains and associated rotary switch means being included in series in an electric circuit in such manner that as the switch means of one series chain of a pair is operated to increase the resistance in the electric circuit the switch means of the other series chain of the same pair is operated simultaneously to decrease the resistance in the electric circuit by an equal amount, and a plurality of concentric operating shafts each connected to the rotary switch means associated with a difi erent pair of first and second series chains.

4. The potentiometer-rheostat of claim 3 including an interpolating potentiometer connected at its opposite ends to the rotary switch means associated with the last succeeding matching pair of first and second series chains, respectively, and including a rotary section arranged coaxial with the rotary switch means, and a rotary opera-ting shaft connected to the rotary section of the potentiometer and arranged concentric with the operating shafts of the rotary switch means.

5. A potentiometer-rheostat comprising a first series chain of resistances of equal value, a second series chain of resistances of equal value and matching the first series chain, a first interpolating resistance associated with the first series chain and having a resistance value one-half the value of each resistance in the first series chain, a second interpolating resistance associated with the second series chain and having a resistance value one-half the value of each resistance in a second series chain, first switch means associated with the first series chain and first interpolating resistance and operable to connect one end of the first interpolating resistance to one end at a time of each resistance in the associated chain and altor-nately between said connections to short out the first interpolating resistance, and second switch means associated with the second series chain and the second interpolating resistance and operable to connect one end of the second interpolating resistance to one end at a time of each resistance in the second series chain and alternately between said connections to short out the second interpolating resistance, the matching pair of first and second series chains and associated interpolating resistances and switch means being included in series in an electric circuit in such manner that as the switch means of one series chain is operated to increase the resistance in the electric circuit the switch means of the other series chain is operated simultaneously to decrease the resistance in the electric circuit by an equal amount.

6. The potentiorneter-rheostat of claim including an interpolating potentiometer operatively connected at its opposite ends to the first and second series chains, respectively.

7. The potentiometer-rheostat of claim 6 wherein the first and secondv switch means comprise coaxial rotary switches and the potentiometer includes a rotary section arranged coaxial with the rotary switches, and concentric rotary shafts connected to the rotary switches and rotary section of the potentiometer for operating the same.

8. A potentiometer-rheostat comprising a plurality of interconnected first series chains of resistances, the resistances in each chain being of equal value and the resistances in succeeding chains being a fractional value of the resistances in the next preceding chain, a plurality of interconnected second series chains of resistances each matching a corresponding one of the plurality of first series chain, a first interpolating resistance associated with each first series chain and having a resistance value one-half the value of each resistance in the associated chain, a second interpolating resistance associated with each second series chain and having a resistance value one-half the value of each resistance in the associated chain, first switch means associatedwith each first series chain and first interpolating resistance associated therewith and operable to connect one end of the first interpolating resistance ot one end at a time of each resistance in the associated chain and alternately between said connections to short out the first interpolating resistance, second switch means associated with each second series chain and second interpolating resistance associated therewith and operable to connect one end of the second interpolating resistance to one end at a time of each re- I sistance in the associated chain and alternately between said connections to short out the second interpolating resistance, the matching pairs of first and second series chains and associated interpolating resistances and switch means being included in series in an electric circuit in such manner that as the switch means of one series chain of a pair is operated to increase the resistance in the electric circuit the switch means of the other series chain of the same pair is operated simultaneously to decrease the resistance in the electric circuit by an equal amount.

9. The potentiometer-rheostat of claim 8 including an interpolating potentiometer operatively connected at its opposite ends to the last succeeding macthing pair of first and second series chains, respectively.

10. The potentiometer-rheostat of claim 9 wherein the.

first and second switch means comprise coaxial rotary switches and the potentiometer includes a rotary section 8. arranged coaxial with the rotary switches, and aplurality of concentric rotary shafts each connected to a different pair of first and second switches, and a rotary shaft connected to the rotary section of the potentiometer and arranged concentric with the rotary shafts of the rotary switches.

11. The potentiometerrheostat of claim 9 wherein each resistance in each succeeding series chain is one-tenth the value of each resistance in the next preceding series chain, and the interpolating potentiometer is one-half the value of each resistance in the last succeeding matching pair of series chains.

12. A- rheost-at comprising a plurality of resistances of equal value connected together in series, an interpolating resistance having a value one-half the value of each resistance in the series chain, and switch means associated with the series chain and interpolating resistance and operable to connect one end of the interpolating resistance to one end at a time of each resistance in the series chain and alternately between said connections to short out the interpolating resistance.

13. A rheostat comprising a plurality of interconnected series chains of resistances, the resistances in each chain being of equal value and the resistances in succeeding chains being a fractional Value of the resistances in the next preceding chain, an interpolating resistance associated with each series chain and having a resistance value one-half the value of each resistance in the associated chain, and switch means associated with each series chain and interpolating resistance associated therewith and operable to connect one end of the interpolating resistance to one end at a time of each resistance in the associated chain and alternately between said connections to short out the interpolating resistance.

14. The rheostat of claim 13 wherein the switch means comprise coaxial rotary switches, and a plurality of concentric rotary shafts each connected to a different rotary switch for operating the same.

15. The rheostat of claim 14 including an interpolating potentiometer connected in series to the last succeeding series chain and including a rotary section arranged coaxial with the rotary switches, and a rotary shaft connected to the rotary section of the potentiometer and arranged concentric with the rotary shafts of the rotary swiches.

References Cited in the file of this patent UNITED STATES PATENTS 1,104,821 Smith July 28, 1914 2,670,422 Baum et al Feb. 23, 1954 FOREIGN rwrnurs 196,613 Great Britain Apr. 17, 1923 

